Background: Professionalism in medical students is not only difficult to define but difficult to teach and measure. As negative behaviour in medical students is associated with post-graduate disciplinary action it would be useful to have a model whereby unprofessional behaviour at the undergraduate level can easily be identified to permit appropriate intervention. We have previously developed a scalar measure of conscientiousness, the Conscientiousness Index (CI), which positively correlates to estimates of professional behaviour in undergraduate medical students. By comparing CI points awarded in year 1 and year 2 of study we were able to use the CI model to determine whether teaching and clinical exposure had any effect on students’ conscientiousness. Methods: CI points were collected by administrative staff from 3 successive cohorts of students in years 1 and 2 of study. Points were awarded to students for activities such as submission of immunisation status and criminal record checks, submission of summative assignments by a specified date and attendance at compulsory teaching sessions. CI points were then converted to a percentage of maximal possible scores (CI %) to permit direct comparison between years 1 and 2 of study. Results: CI % scores were generally high with each year of study for each cohort showing negatively skewed normal distributions with peaks > 89%. There was a high degree of correlation of CI % scores between year 1 and year 2 of study for each cohort alone and when cohort data was combined. When the change in CI % from year 1 to year 2 for all students was compared there was no significant difference in conscientiousness observed. Conclusions: We have provided evidence that use of a CI model in undergraduate medical students provides a reliable measure of conscientiousness that is easy to implement. Importantly this study shows that measurement of conscientiousness by the CI model in medical students does not change between years 1 and 2 study suggesting that it is a stable characteristic and not modified by teaching and clinical exposure.